
<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title>demo</title>
	<style type="text/css">
		*{
			margin: 0;
			padding: 0;
		}
		.area{
			position: fixed;
			display: none;
			left: 50%;
			top: 50%;
			transform: translate(-50%,-50%);
			background-color: rgba(0,0,0,0.3);
		}
		.closeBtn{
			width: 30px;
			height: 30px;
			position: absolute;
			right: 0;
			top: 0;
			border: none;
			outline: none;
		}
		.closeBtn:hover{
			background-color: rgba(255,0,0,0.3);
			color: white;
			cursor: pointer;
		}
	</style>
</head>
<body>
	<form method="" action="">
		<button type="button" class="login">登录</button>
	</form>
	<div class="area">
		<button class="closeBtn">x</button>
	</div>
 
	<script type="text/javascript">
		window.onload = function(){
			function getByClass(classname){
				return document.getElementsByClassName(classname);
			}
			var login = getByClass("login")[0];
			var area = getByClass("area")[0];
			var closeBtn = getByClass("closeBtn")[0];
			// 显示
			login.addEventListener("click",show,false);
			function show(){
				var client_width = document.body.clientWidth || document.documentElement.clientWidth;
				var client_height = window.screen.height;
				area.style.cssText = "display:block;width:"+client_width/2+"px;height:"+client_height/2+"px;"
			}
			// 关闭
			closeBtn.addEventListener("click",close,false);
			function close(){
				area.style.cssText = "display:none";
			}
			// 点击其他位置关闭
			document.onclick = function(event){
				if(area.style.display == "block" && event.target.className != "login"){
					if(event.target.className != area){
						close();
					}
				}
			}
			//阻止冒泡
			area.addEventListener("click",function(event){
				var event = event || window.event;
				var target = event.target || event.srcElement;
				event.stopPropagation();
			})
		}
	</script>
</body>
</html>
